The present invention relates in general to brakes for land vehicles, and, more particularly, to bicycle brakes.
There are several drawbacks inherent in those brakes presently used with bicycles. Among these drawbacks are the following.
If the brake is mounted on the front wheel, that brake is mounted in front of the bicycle front fork. This type of mounting generates chatter and is mechanically unsound because a bad bending moment is placed on the bolt attaching the brake to the bicycle frame. Such bending moment may eventually cause the bolt to crack or break. Such forward mounting also transfers no positive braking forces into the bicycle frame except via bolt bending. Furthermore, such forward mounting exposes the brake to dirt and the like, as well as exposes that brake to damage due to collision, or cargo being carried on the bicycle, or the like.
A further drawback inherent with presently available bicycle brakes results because the mounting bolt is the main point for mounting the brake. Thus, the distance between the mounting bolt at the fork or rear stay varies considerably with the wheel size, frame size, and the like, and the support bracket that holds the brake shoe has to be designed to carry considerable leverage forces. In many cases, the reach is considerable. At the extremities of the reach, when the brakes are applied, very bad twisting and consequent chatter of the brake shoes becomes apparent. All presently available brakes are designed to have a single supporting arm, and the brake pad and brake block support is mounted on one side of the support arm. This offset causes detrimental torsional forces. If the arms are designed and made strong enough and heavy enough to counteract most of these forces, these arms become unduly large and heavy. The wide range of frames as marketed, and wheel sizes, and rim angles makes it very difficult to accommodate these varied conditions with presently available bicycle brakes.
Most of the presently known hydraulic bicycle brakes utilize two cylinders. The use of two cylinders causes several problems. First, a considerable amount of weight is added by the presence of an extra cylinder. Two cylinders generally encumber the brake unit and make it vunerable to damage due to the far-reaching appendage of the unit. Such vulnerability merely doubles maintenance problems and initial costs involved with such units. Size and weight, both being major factors in bicycles, are important considerations detrimentally affected by the use of two cylinders. A large master cylinder is required to supply both of the slave cylinders, and thus the size and weight of such units is increased as compared to a unit using only a single slave cylinder.
It is noted that in reality, there are no hydraulic bicycle brakes available today on the market. The Shimano brake has a reservoir system similar to that in an automobile, and it occasionally, especially when the bike is roughly handled or tipped over, has air in the system. This happens quite often, and requires proper bleeding and servicing. In order to perform this service, a man had to be a hydraulic expert. This presents the problem of installing a sufficient number of repair stations to service the brake. Also, the brake has not shown good acceptance because of its very heavy and clumsy appearance.
Many presently known bicycle brake units include factory sealed systems. Such systems present still further drawbacks. For example, on brake units with factory sealed systems, no field or owner maintenance can be performed.
U.S. Pat. No. 3,776,333 discloses a brake with a sealed system. Where this device does not have the servicing problems that the Shimano had, it has other disadvantages. In actual service, it was found that a system that was indeed sealed had to be replaced in its entirety if any damage occurred within the system, such as a broken line, leak, or the like. Secondly, it was found that within the system, any flexible portion thereof, such as the flexible hydraulic line itself, has one inherent characteristic. Any flexible material that is carrying fluid under pressure constantly has a tendency to bleed and have permeability. In time, depending on pressure and temperature, the brakes lose their effectiveness and may become quite dangerous. There is no known way of coping with this condition. Also, this requires dealers to carry a series of different lengths of hydraulic lines to accommodate various sizes of bicycles. Another disadvantage of the device disclosed in this patent is the cost and limited life of the bellows. There is a definite limit of travel in the bellows, and if this is extended, overstressing of the bellows and an extremely short life will result.
One presently known brake unit is disclosed in U.S. Pat. No. 3,935,927. However, the device disclosed in this patent has several drawbacks. First, the system disclosed in this patent is virtually a fixed system in that it allows for no adjustment other than horizontal. The patented system is inherently very heavy, and therefore is not a practical brake for bicycles. It is here noted that, with the exception of heavy tandem-type machines where two, three or four people are riding on them, use of a disc-type brake is not possible. Such heavy machines use heavy wheels and heavy spokes to allow the forces from a disc mounted at the hub to be transferred to the outer periphery of the wheel. When a disc is mounted as just mentioned on a conventional bicycle, and an effort is made to stop the bicycle from the center of the wheel, such as in the patented disc brake, it subjects the nipples, the spokes and the rim to pressures and forces that these elements are not designed to withstand if the weight of the bicycle is to be kept within practical limits. It is here noted that the heaviest drag on a bicycle is that of the periphery of the wheel and the outer extremities of the wheel. Tires, rims, spokes, and the like should, therefore, be as light as possible. As braking forces are applied closer to the outer periphery of a wheel, these forces become more effective and less pressure is required. Thus, the forces necessary to stop a wheel in the center as disclosed in the just-referenced patent far exceed such forces as applied at the outer circumference of that same wheel. In order to induce such stopping forces in the patented device, a considerable amount of weight in material alone is required. In motorcycles, where weight is not an important criteria, the patented brake may be practical, as in nearly all cases, the brake is actuated by a rider's foot, and ample leverage and pressure can be generated. However, in a hand brake, since there is so little energy or forces which can be generated by a rider's hand, it is imperative that as little loss as possible occurs between the hand pressures and the pressures generated at the brake pad.
A further prior art brake system is known as the Shimano-type brake system. The Shimano system is a reservoir-type hydraulic system. This, on a bicycle, has proven to be undesirable. It uses a wet cylinder similar to that in a car, and, of course, a certain amount of dripping and bleeding is always prevalent. Secondly, with a so-called "open-system", any air entrapment in the system from the bicycle tipping over, or the like, causes difficult problems. The brake is no longer being manufactured because of this vulnerability to ingesting air into the system.
Furthermore, presently known bicycle braking devices are difficult and expensive to manufacture. Often it takes as much as 30 minutes line time to assemble such devices. This lengthy assembly time is caused because appendages or cables are positioned and welded on various positions of the frame. Other brackets and fittings are also painstakingly welded to the frame and the cable is carefully put through small eyelets and leads. The brake is finally installed in its proper position. The cables are then adjusted, tightened and cut, and the brake aligned and adjusted in its final form. There seems to be no quick way of executing the above steps.
Yet a further disadvantage to known brakes results because of the gripping requirements of hand operated hydraulic brakes. In all mechanical, cable brakes marketed and in use today, in order to get sufficient braking force and to compensate for friction within the system, the lever handle, or arm, must have within its design as much lever action as practical. Usually a 5 or 6 to 1 leverge ratio is all that can be designed into this type of system. The Campagnolo brake, for example, has a distance of 21/2 inches between the handlebar and the back of the lever handle. If one has a large hand, and is capable of pulling the brake, one can get adequate stopping conditions. However, small-handed children and women do not have that reach or that power to properly stop the bicycle. This means in order to brake a bicycle, especially if it is loaded, the small-handed person must reach out and simply pull the handle itself. This is not a squeezing action and is very dangerous to do, but is simply the only way such a person can stop the bicycle. Squeezing between the thumb and forefinger is the only practical way of controlling the forces.